With broadening uses of mobile products such as a mobile phone and a personal digital assistant (PDA), various attempts to reduce the current consumption of a semiconductor memory device mounted on such mobile products have been continuously made. In particular, reducing a refresh current of a semiconductor memory device for mobile products is becoming a big issue.
The Dynamic Random Access Memory (DRAM) has such a characteristic that information stored in memory cells eventually fade unless the capacitors of the memory cells are recharged periodically, and the recharging operation is referred to as refresh operation. The refresh operation is performed as follows: a word line is activated at least one time within a data retention time of the memory cell in order to sense and amplify the data. Here, the data retention time refers to a time during which data can be retained in a cell without refresh, after the data is written in the cell.
The refresh operation includes auto-refresh operation which is performed during a normal operation and self-refresh operation which is performed in a power down mode or the like. Here, the self-refresh operation is performed by a self-refresh signal which is generated by a command decoder receiving a command signal. That is, when a self-refresh signal is enabled for self-refresh operation, a periodic signal generated by a self-refresh oscillator is outputted according to a self-refresh period.
FIG. 1 is a block diagram illustrating the configuration of a known semiconductor memory device performing refresh.
Referring to FIG. 1, the known semiconductor memory device includes an address counter 11 and a row decoder 12. The address counter 11 is configured to receive a start signal CNT which is enabled when an auto-refresh command or self-refresh command is inputted, and count refresh addresses RAT<1:N>. The row decoder 12 is configured to decode the refresh addresses RAT<1:N> and generate row addresses XADD<1:2N> for refreshing a memory cell array 13.
According to an example, the refresh of the semiconductor memory device configured in such a manner generates 2N row addresses XADD<1:2N> whenever an auto-refresh command or self-refresh command is inputted. Therefore, if the memory cell array 13 includes 4*2N memory cells, four memory cells may be simultaneously refreshed whenever the address counter 11 counts the refresh address RAT<1:N>.
However, refresh frequency needs to be controlled depending on the temperature. That is, at low temperature where the data retention time increases, the refresh frequency may be decreased to reduce current consumption, and at high temperature where the retention time decreases, the refresh frequency may be increased to reduce a probability of a refresh fail. However, the refresh of the known semiconductor memory device perform the refresh operation constantly regardless of the temperature change, e.g., generates 2N row addresses XADD<1:2N> whenever an auto-refresh command or self-refresh command is inputted.